Pesticide Note Number 8
ENT/pia-8
December 1998

Insect Management by North Carolina Sweetpotato Growers in 1996

Kenneth A. Sorensen, Extension Vegetable Entomology Specialist

Introduction

North Carolina led the United States in sweetpotato production in 1996. Growers in the state produced 434 million pounds of sweetpotatoes valued at $46.4 million (Meadows 1997). Sweetpotato production in North Carolina is concentrated in the coastal plain (Wilson et al. 1989). Sweetpotato plants are generally transferred from plant beds to the fields in May and June and harvested from September to October. A variety of insect pests are injurious to sweetpotato plants in plant beds and the field and to sweetpotatoes held in storage.

A mail survey of sweetpotato growers in twenty-two counties in North Carolina was conducted in the winter of 1997 to determine the pest management practices used by sweetpotato growers on the 1996 crop. Insect management practices used by survey respondents in 1996 are reported with results from a similar grower survey conducted for the 1991 crop (Toth et al. 1996).

Survey Method

A total of 613 commercial sweetpotato growers from Brunswick, Chowan, Columbus, Cumberland, Duplin, Edgecombe, Greene, Halifax, Harnett, Johnston, Lee, Lenoir, Moore, Nash, Onslow, Pitt, Richmond, Robeson, Sampson, Wake, Wayne and Wilson counties (Fig. 1) were surveyed by mail in March and April 1997, following methods described by Christenson (1975) and Dillman (1978). Mailing lists of sweetpotato growers were obtained from the North Carolina Consolidated Farm Services Agency and the North Carolina Sweetpotato Commission. Information collected from survey respondents was compiled and analyzed in the Department of Entomology at North Carolina State University.

Results and Discussion

Sweetpotato Production: Of the 613 sweetpotato growers surveyed, 311 or 51% responded. The respondents cumulatively planted 19,609 acres of sweetpotatoes in 1996. Approximately 33,000 acres of sweetpotatoes were planted in North Carolina in 1996 (Meadows 1997). Beauregard (9,682 acres), Hernandez (6,842 acres) and Jewel (1,816 acres) were the most common sweetpotato varieties planted by growers responding to the survey. The respondents harvested a total of 18,222 acres of sweetpotatoes in 1996. Statewide, 31,000 acres of sweetpotatoes were harvested in 1996. One bushel equals approximately 50 pounds of sweetpotatoes. The average yield by survey respondents growing sweetpotatoes in 1996 was 255 bushels (127.5 cwt.) per acre. By comparison, the average yield of growers in the entire state in 1991 was 140 cwt. per acre. Growers also reported the number of square feet of sweetpotato plant beds they planted in 1991, which totaled 29,301,441 (673 acres). One acre of sweetpotato plant bed provides a sufficient number of plants for 29 acres of sweetpotato fields (Monks et al. 1992).

Insect and Mite Pests of Sweetpotatoes: Approximately 66% of survey respondents used insecticides to manage insects in sweetpotato plant beds and fields in 1996. The primary insect pests for which insecticides were used by survey respondents in 1996 were wireworms (76% of the respondents using insecticide), white grubs (40%), whitefringed beetle larvae (24%), flea beetles (21%), flea beetle larvae (17%), and tortoise beetles (5%).

Foliage-feeding Insects: Under average conditions, insect damage to sweetpotato foliage is not severe enough to justify treatment with insecticides (Wilson et al. 1989). However, flea beetles, tortoise beetles, leafhoppers, leafminers, corn earworms, hornworms, armyworms and loopers can cause significant damage in plant beds and to small plants in the field. Growers reported very little use of insecticides in plant beds or for management of foliar-feeding insects in sweetpotato fields in 1996. Thiodan, Lorsban, and Dyfonate were each used by survey respondents on less than 5% of their plant bed acreage, while Thiodan was used on 1% of the sweetpotato field acreage in 1996. Sweetpotato growers used Sevin on less than 2% of the plant bed acreage
and 3% of the field acreage in 1991 (Toth et al. 1996).

Root-feeding Insects: Insects that feed on the roots of the sweetpotato plant include flea beetle larvae, wireworms, white grubs, and whitefringed beetle larvae. Among survey respondents, 80% of the sweetpotato field acreage in 1996 was treated with Lorsban for management of root-feeding insects (Fig. 2). Lorsban is broadcast and incorporated in the soil before planting. Dyfonate and diazinon are applied to the soil before planting or at midseason to manage root-feeding insects. Dyfonate was used on 69% of the acreage in 1996, while diazinon was used by growers on less than 1% of the acreage. Dyfonate is no longer sold and growers are
looking for other methods of managing root-feeding insects. Mocap and Thiodan were used on 4 and 2% of the acreage, respectively, in 1996.

Integrated Pest Management Practices: Monitoring insects is important for the management of both foliar-feeding and root-feeding insects on sweetpotatoes. Fifty-seven percent of the survey respondents reported walking their sweetpotato fields to scout for insects and their damage. Only 4% of growers used light traps to monitor insects and less than 2% used seed baits in the soil to detect insects in 1996. Crop rotation is an effective management practice for root-feeding insects. Ninety-six percent of growers claimed to have rotated crops in the fields where they grew sweetpotatoes in 1996. The crops rotated with sweetpotatoes include tobacco,
soybeans, corn, cotton, wheat, and peanuts.

Sweetpotato Weevil: The sweetpotato weevil, a serious insect pest of sweetpotato, is not present in the commercial sweetpotato-producing areas of North Carolina. However, the weevil is established in coastal areas near Wilmington where it can be found on seaside morningglory. The adult weevil can feed on any part of the sweetpotato plant, but prefers stored roots. The larvae feed on the roots.

To prevent this destructive insect pest from becoming established in the state, growers are advised to use only certified seed or plants produced in North Carolina or noninfested areas. Traps containing a sex pheromone are used in plant beds, fields and storage houses to detect adult male weevils. Forty-three percent of survey respondents used these traps in 1996, compared to only 7% in 1991.

Literature Cited

Christenson, J. A. 1975. A procedure for conducting mail surveys with the general public. J. Community
Development Society 6(1): 135-146.

Dillman, D. A. 1978. Mail and Telephone Surveys: The Total Design Method. John Wiley and Sons, New
York. 325 pp.

Recommendations for the use of chemicals are included in this
publication as a convenience to the reader. The use of brand names
and any mention or listing of commercial products or services in
this publication does not imply endorsement by the North Carolina
Cooperative Extension Service nor discrimination against similar
products or services not mentioned. Individuals who use chemicals
are responsible for ensuring that the intended use complies with
current regulations and conforms to the product label. Be sure to
obtain current information about usage and examine a current
product label before applying any chemical. For assistance,
contact an agent of the North Carolina Cooperative Extension
Service in your county.

Employment and program opportunities are offered to all people regardless of
race, color, national origin, sex, age, or disability. North Carolina State
University at Raleigh, North Carolina A&T State University, U.S. Department of
Agriculture, and local governments cooperating.